This invention relates to an information processing system comprising a main memory, at least one standard processor, a system controller, and a diagnostic processor. The standard processor is, for example, a control processor, an arithmetic processor, or the like.
In an information processing system of the type described, the diagnostic processor comprises a diagnosing unit connected to the main memory, the standard processor, and the system controller. The diagnosing unit carries out a diagnosing operation on the main memory, the standard processor, and the system controller in response to an activation signal. Connected to the diagnosing unit, a monitoring unit detects a failure in the diagnosing unit, namely, it monitors the diagnosing unit to produce a state signal indicative of whether or not the diagnosing unit can carry out the diagnosing operation. Connected to the diagnosing unit and the monitoring unit, a diagnosis control unit carries out a controlling operation for restart or retry of the diagnosing operation in response to the state signal when the state signal indicates that the diagnosing unit can not deal with the diagnosing operation. Such a controlling operation of retry for the diagnosing operation will later be described.
It will be assumed that the information processing system comprises first and second standard processors. Each of the first and the second standard processors can put the diagnosing unit into a normal state of carrying out the diagnosing operation by sending, as the activation signal, a communication request signal to the diagnosing unit through the system controller. For example, the communication request signal is sent to inform the diagnosing unit that a failure has occurred in the standard processor in question. Alternatively, the communication request signal is sent to make a request for a log-out which is known in the art. It will also be assumed that the diagnosing unit is put in the normal state by a first communication request signal sent by the first standard processor and that the monitoring unit finds a failure to put the diagnosis control unit into the controlling operation for retry of the diagnosing operation. In this event, the diagnosing unit is temporarily put in an interrupted state for interrupting the diagnosing operation.
It will furthermore be assumed that the second standard processor sends, as the activation signal, a second communication request signal to the diagnosing unit through the system controller while the diagnosing unit is kept in the interrupted state.
In a conventional information processing system, the system controller reserves, in such a case, the second communication request without delivering the second communication request signal from the system controller to the diagnostic processor until the diagnosing operation is fully retried. In many cases, the second standard processor can not receive a reply communication signal from the diagnosing unit through the system controller within a predetermined time duration after the second communication request signal is sent to the system controller. Therefore, the second standard processor is subjected to a time-out error. This puts the information processing system into a system down state.